Gallium nitride (GaN) is a novel radio frequency (RF) power transistor and has lots of advantages. However, a GaN RF transistor needs a negative bias voltage and a high drain voltage. In order to enable a GaN RF power amplifier to work safely, several problems as listed below need to be solved.
First, upon powering on, an accurate negative bias voltage needs to be applied to the bias circuit, then a high positive voltage is applied to the drain of the GaN power transistor, and finally an RF signal is turned on. Otherwise, the GaN power transistor will be damaged in the power-on stage. Second, upon powering off, the RF signal needs to be firstly turned off, then the high positive voltage on the drain of the GaN power transistor is switched off, and finally the negative bias voltage is disconnected. Otherwise, the GaN power transistor will be damaged in the power-off stage.
Third, the negative bias voltage needs to provide a sufficient large current, otherwise the GaN power transistor will be damaged when overdriven, which usually takes place in a mobile communication environment. Fourth, a turning on speed of the high positive voltage on the drain should be reasonably slow, otherwise an inrush current upon turning on the GaN power transistor will be very large, and it will destroy the GaN power transistor if ON/OFF is performed for several times. On the other hand, when the power amplifier is turned off, a turning off speed of the high positive voltage on the drain should be quick enough. Otherwise, the GaN power transistor may be easily damaged in the power-off stage if ON/OFF is performed for several times.